Step 1: Measure and Mark the Wood

Measure the width of the first piece of wood. In this case, the lumber is 2" x 2", so the actual width is 1-1/2". Use a pencil and ruler to mark a spot at one edge of the end that is one-third the total width of the wood -- in this case 1/2".

Step 2: Mark the Long Edge of the Wood

Working on the side closer to the mark made in step 1, use the ruler to mark a spot on the long edge of the wood that is three times the total width of the wood. In this case, the mark should be 4-1/2" from the short edge.

Step 3: Make a Perpendicular Mark

From the point marked in step 2, position the ruler perpendicular to the wood, and mark a spot two-thirds the width of the lumber. In our example, that would be 1", as the wood is 1-1/2" wide.

Step 4: Draw a Line

Using the ruler as a straightedge, draw a line between the marks made in steps 1 and 3.
Repeat steps 1 through 4 for the second piece of wood.

Step 5: Adjust the Blade and Fence

Adjust the height of the table-saw blade to two-thirds the width of the wood. Adjust the table-saw fence so the work piece hits the blade at the mark made in step 3.

Step 6: Send the Pieces Through the Blade

Hold the two pieces of wood together so that the pencil tracings on both face you. Send both pieces through the blade at the same time.

Step 7: Make the Long Cut, and Secure the Joint

To make the long cut for the joint, hold the two pieces of wood together so their pencil marks face up. Send the wood through a band saw, guiding the blade down the pencil line.
Fasten the joint with glue, then secure it with wood screws.